The collet used to secure the work in an automatic bar machine, screw machine, or the like, is normally closed by shifting an outer spindle over an enlarged forward end portion of the collet. The means for shifting the outer spindle is generally referred to as the "collet closing mechanism," and for many years the most widely used mechanisms of this sort comprised an arrangement of chuck levers mounted in a chuck lever fulcrum. So-called "ball-chucker" systems have also been provided in which a circular array of ball bearings, held within a cage behind a slidably mounted thrust collar, are forced by an outer, slidably mounted sleeve into a circumferential channel defined behind the collar, so as to shift it forwardly.
More recently, a highly effective and durable collet closing mechanism has been provided in which a circular array of wedges provide force-transmitting elements. Such a mechanism, and improvements thereto, are described and claimed in Nowak U.S. Pat. No. 4,418,925, issued Dec. 6, 1983, No. 4,509,765, issued Apr. 9, 1985, and No. 4,995,625, issued Feb. 26, 1991. Despite the attributes of the Nowak mechanism, it would of course be beneficial to realize further improvements in effectiveness, operation, and cost and facility of manufacture.